ESR studies on C<inf>60</inf>.O<inf>x</inf> and C<inf>60</inf>.HMTTEF

The electron spin resonance (esr) of C60.Ox and C60.HMTTEF (hexamethylentetratellurafulvalene) has been investigated at 9.36 GHz as a function of temperature, T (298 ≥ T ≥ 4 K). C60.Ox shows an esr absorption of equal 'g' value to that of C6 0 exposed to O2 and light but is more intense. The C60 in its pure form is in a singlet state. The impurity sites introduced by O2 produce the esr absorption. The Curie - Weiss plots of inverse esr absorption intensity versus temperature indicate an antiferromagnetic Θ ≈ 50 for air exposed C60 and 90K for C60Ox. From the esr intensity at room temperature, the calculated number of free spins (S = 1/2) is ≈ 1/3 per mole of C60.Ox. In case of C60.HMTTEF, there is a very weak esr absorption at room temperature suggesting that the room temperature form is diamagnetic with very small charge transfer between C6 0 and HMTTEF. This conclusion is consistent with the structure and magnetic susceptibility of this cocrystal. As the temperature is lowered, the equilibrium: AD <=> A*- + D*+ is displaced towards the formation of free radical species, A*- and D*+.